The effectiveness of an orthopaedic implant often depends upon the presence of an irregular surface on the implant, into which the bone may grow to create a natural joinder between the bone and the implant. Several techniques have been used to create implants with irregular surfaces. Grit blasting is one surface roughening technique, but grit blasting can cause significant changes to the surface topography by damaging the metal elements (e.g., beads) on the surface layer of the substrate. Other mechanical roughening techniques, such as scratching or burr grinding, have also been used. These techniques can also present drawbacks, including distortion of the substrate, removal of excess material, inability or difficulty to roughen certain surfaces, and inconsistent surface roughening.
Electrochemical or chemical etching techniques have also been used to roughen the surface of an implant. Chemical etching often involves using toxic reagents, such as methanol, or a strong acid at a high temperature (as high as 80° C., for example), or strong acid mixtures. Chemical etching, even under these stringent conditions, can require several hours to several days to roughen a surface. Chemical etching also presents the potential for preferential etching on grain boundaries, which can reduce the mechanical properties of the implants
Furthermore, the surface roughening of certain implants made with a cobalt-chromium alloy can be difficult because of the corrosion resistance of chromium.
Accordingly, there remains a need for improved and reliable methods to form an effective textured surface on a metal or metal alloy substrate. There is also a need for orthopaedic implants having a surface texture.